I think the best approach would be to only save a post meta value ( [or use a custom table][1] ) which indicates that a video upload should happen. Also register a schedule that will query for all posts that are marked as “upload needed” and do the upload in the schedule execution.
https://gist.github.com/EdwardBock/85c971633ea1abf8f248f4fb468344ed
You can shorten the schedule timings ( Cron schedule interval through plugin options? ) but make shure to separate your visitors requests from schedule execution by moving it to a real cron job.